Pouches or containers are used today for transporting or storing various products. In such a pouch or container, the properties of the material that forms the pouch or container has a great influence on the storage stability of the content or ease of transportation thereof.
Vertical pouch form fill machines are configured to form pouches from a packaging material (multilayer material) and fill the pouches with content. The vertical pouch form fill machines have the advantage of being capable of packing various foods or beverages. In addition, the packaging material has less opportunity to be touched by human hands in the vertical pouch form fill machines, which allows sanitation and labor savings to be achieved. Therefore, the vertical pouch form fill machines are widely used. In the vertical pouch form fill machines, a multilayer material supplied from a roll of the multilayer material (packaging material) is formed into a tube in a sailor collar-like section, and then the body part of a pouch is sealed. Subsequently, the bottom part of the pouch is sealed. Next, a measured amount of content is dropped from above the pouch so as to be filled into the pouch. Then, the upper part of the pouch is sealed, the upper edge of the sealed upper part is cut, and the pouch is introduced to a discharge conveyor. In this way, the pouch form fill machines perform a series of steps from the step of forming a pouch to the step of discharging the pouch filled with content.
In the case where the content is something that is deteriorated by oxygen gas, packaging materials having oxygen barrier properties are used for the vertical form fill seal pouch. Examples thereof to be used include a multilayer material that includes a film with barrier properties, such as aluminum foil, a coextruded polyamide film with barrier properties, a polyvinylidene chloride resin film, a film composed of ethylene-vinyl alcohol copolymer (hereinafter also referred to as “EVOH”), an aluminum deposited film and an inorganic material-deposited film. However, all those barrier films each have a problem as follows.
In the case of using a packaging material including aluminum foil, it is difficult to detect foreign substances in the content with a metal detector or by visual inspection. Further, the packaging material cannot be used in a microwave oven. Furthermore, aluminum clusters remain in the incineration process after disposal, which also is a problem.
Packaging materials using a polyvinylidene chloride resin film may be insufficient in oxygen barrier properties when the content is something that undergoes significant deterioration due to oxygen gas, though they may be sufficient in oxygen barrier properties, depending on the content. Furthermore, there are cases where a toxic gas such as dioxin is generated in the incineration process, resulting in environmental pollution.
Packaging materials using an EVOH film have a problem that their oxygen barrier properties are deteriorated when the EVOH film absorbs moisture, while this film exhibits excellent oxygen barrier properties in a low humidity atmosphere.
As a gas barrier film having excellent oxygen barrier properties, there are aluminum deposited films, and inorganic material-deposited transparent films formed by depositing silicon oxide, aluminum oxide, or the like. However, when such films are used in the vertical pouch form fill process, there is a problem that the barrier performance is deteriorated due to the generation of cracks or pinholes in the gas barrier layer (inorganic material-deposited layer).
As a packaging material that solves the above-mentioned problems, there is proposed a packaging material including a base, a substrate film and a sealant layer, in which a thermoplastic resin layer is disposed between the base and the substrate film (JP 5(1993)-318550 A). JP 5 (1993)-318550 A describes that the thermoplastic resin layer suppresses the deterioration of the oxygen barrier properties and water vapor barrier properties. However, the deterioration in the barrier performance is still not sufficiently suppressed.
In the vertical pouch form fill machine, when the packaging material is formed into a tube in the sailor collar-like section, the packaging material is stretched while being bent and held in contact with the edges of the sailor collar-like section. Further, there are cases where the packaging material deforms when content is filled therein. Furthermore, the packaging material may be squeezed in some cases so that the air in the headspace of the pouch is eliminated. Thus, the packaging material to be used in the vertical pouch form fill machine is required to have properties that are less deteriorated when being subjected to the above-mentioned process.
Moreover, today, there is an increasing number of cases of harsh conditions (time, temperature, humidity and the like) during the period from pouch form filling/heat sterilization to arrival at a consumer area. For example, foods that have been filled and packed in Southeast Asia, South America, etc. are transported to Europe and the United States, Japan, etc. Therefore, a vertical form fill seal pouch that stably exhibits a high level of oxygen barrier properties even under severe conditions of transportation, etc. is desired.
Furthermore, covered containers each composed of a cover and a tray or a cup having a flange are often used today as a container for storing content such as foods. In such covered containers, not only the containers such as cups and trays but also the covers are required, depending on the type of content, to have oxygen gas barrier properties. Thus, the use of a layered product including a film with excellent oxygen gas barrier properties as the cover has been conventionally proposed. For example, a polyvinylidene chloride resin film, an EVOH film, and a deposited film in which a deposited layer of inorganic substances such as silica, alumina and aluminum is formed on a base film (hereinafter also referred to as a “deposited film”) have been used as the film with excellent oxygen gas barrier properties. A cover including a polyvinylidene chloride resin film (JP 57(1982)-30745 B2) and a cover including an EVOH film (JP 9(1997)-239911 A), for example, are proposed.
Further, a cover including an inorganic material-deposited layer also has been proposed (JP 2005-8160 A). However, such a cover has a problem that gas barrier properties are easily deteriorated due to the generation of cracks in the inorganic material-deposited layer. In response to this, there has been proposed a cover for a boil-in/retort container in which an anchor coat agent layer, a deposited film of an inorganic oxide, and a gas barrier coating film that has been obtained by sol-gel method are stacked on a base film (JP 2008-044617 A). There also has been proposed a cover in which a transparent gas barrier deposited layer composed of an inorganic oxide, a gas barrier coating layer, and a heat sealing resin film are stacked on a polyester film (JP 2006-027695 A). Further, there has been proposed a cover in which an anchor coat layer, a deposited thin film layer of an inorganic oxide, a gas barrier coating layer, and a sealant layer are stacked on a biaxially stretched polyamide film (JP 2005-231701 A). In such covers, the gas barrier coating layer can prevent the inorganic material-deposited layer from cracking. However, it is still difficult to completely prevent the inorganic material-deposited layer from cracking, in these covers. Depending on the intended use, there are the cases where the inorganic material-deposited layer cracks. For example, when the content includes the air, the cover is significantly inflated in boiling sterilization at atmospheric pressure, so that the cover is easily damaged. Further, the cover tends to shrink more easily in retort sterilization at high temperature, so that the cover fixed to the flange is easily stretched and damaged particularly in the periphery of the flange.
The inventors have proposed a container cover that suppresses the deterioration of the oxygen barrier properties resulting from physical impact or deformation in processing or transportation (JP 2006-306083 A).
Meanwhile, under severe heat sterilization conditions, such as the conditions where a covered container with a content including the air is subjected to boiling sterilization at high temperature and atmospheric pressure or retort sterilization at high temperature for a long time, the oxygen barrier performance is more easily deteriorated due to the deformation of the cover. Moreover, today, there is an increasing number of cases of harsh conditions (time, temperature, humidity and the like) during the period from fill packaging/heat sterilization to arrival at a consumer area. For example, foods that have been filled and packed in Southeast Asia, South America, etc. are transported to Europe and the United States, Japan, etc. Therefore, a cover that stably exhibits a high level of oxygen barrier properties even under severe conditions of boiling sterilization, retort sterilization, transportation, etc. is desired. Furthermore, a cover capable of maintaining its appearance even if it is subjected to a treatment under severe conditions is desired.
Conventionally, vacuum packaging is widely employed as an effective method for suppressing the chemical changes and microbial changes of the content such as corn on the cob (corns), beans, bamboo shoots, potatoes, chestnuts, tea, meat, fish, confectioneries etc. so as to achieve a long shelf life. Although heat sterilization is performed after vacuum packaging in many cases, there also are cases where the vacuum packaging of the content is performed in a sterile state so that the heat sterilization is omitted. In either the cases with or without heat sterilization, it is necessary to keep the oxygen concentration inside the package low, in order to suppress the microbial changes and chemical changes after vacuum packaging over a long period. Therefore, a pouch having high oxygen barrier properties is used for vacuum packaging.
The vacuum packaging pouch having high oxygen barrier properties is formed using a multilayer material that includes an oxygen barrier film. Examples of the oxygen barrier film that have been used include a polyvinylidene chloride resin film, an EVOH film, aluminum foil, and a film having a deposited layer composed of an inorganic oxide such as silicon oxide and aluminum oxide. However, all these oxygen barrier films have a problem as described below, and are not satisfactory as an oxygen barrier film for the vacuum packaging pouch.
With further increasing attention to the environment, the amount of use of a multilayer material that includes a polyvinylidene chloride resin film or a multilayer material that includes aluminum foil is now decreasing. The multilayer material that includes aluminum foil has a problem that aluminum foil remains as residue when being incinerated after the use. Furthermore, the multilayer material that includes a polyvinylidene chloride resin film has a problem of the possibility that a toxic compound containing chlorine is generated when being incinerated after the use. Moreover, it has been pointed out that the multilayer material including aluminum foil has a problem that the state of the content cannot be checked because of its opacity, and that the content cannot be inspected with a metal detector, for example.
The multilayer materials that include a deposited layer of an inorganic oxide such as silicon oxide and aluminum oxide are transparent and have excellent gas barrier properties. However, there are cases, in the multilayer materials, where the gas barrier properties are deteriorated due to cracks or pinholes in the inorganic oxide layer that have been generated by the deformation in vacuum packaging. In other words, there are cases where the deformation of the packaging pouch corresponding to the irregularity of the content, or the bending at the border between the portion in contact with the content and the heat sealed portion causes cracks or pinholes in the inorganic oxide layer. Furthermore, there also are cases where the stretching of the packaging pouch during heat sterilization, or the vibration or drop of the pouch during transportation or handling causes cracks or pinholes in the inorganic oxide layer. As described above, the multilayer material that includes a deposited layer of an inorganic oxide has a problem that the oxygen barrier properties are deteriorated due to the generation of cracks or pinholes.
The layered product that includes an EVOH layer has excellent oxygen barrier properties. However, this layered product has a problem that the oxygen barrier properties are temporarily deteriorated, immediately after heat sterilization that is performed subsequent to the vacuum packaging.
As a container for vacuum packaging having excellent gas barrier properties, there is proposed a container formed of a layered product that is provided with a resin composition layer containing an inorganic layered compound between a heat sealing film and a base layer such as a thermoplastic film (JP 11(1999)-314675 A). However, this container has a problem of insufficient oxygen barrier performance.
Further, there is proposed a packaging material for vacuum packaging a content that is hard and has a projecting portion (JP 2005-119063 A). This packaging material is a layered product of a base layer, a straight chain low density polyethylene resin layer, a gas barrier layer and a sealant layer. Examples of the gas barrier layer mentioned therein include a deposited polyester film on which an inorganic substance (aluminum metal, aluminum oxide or silicon oxide) is deposited, a deposited nylon film, a vinylidene chloride film, an ethylene-vinyl alcohol film, aluminum foil etc. However, such materials to be used for the gas barrier layer have problems as mentioned above. Moreover, the above-mentioned structure does not provide sufficient pinhole resistance.
Further, JP 2006-036272 A discloses a vacuum packaging material that includes aluminum foil and a plastic film on which an inorganic compound is deposited. The plastic film on which an inorganic compound is deposited is used for maintaining the barrier properties even when cracks or pinholes are generated in aluminum foil. However, this vacuum packaging material uses aluminum foil and thus has a problem as mentioned above. Moreover, the plastic film on which an inorganic compound is deposited has a problem that cracks or pinholes are likely to be generated.
In order to solve the above-mentioned problems, the inventors have proposed a vacuum packaging pouch using a specific gas barrier layered product (JP 2007-008148 A).
Meanwhile, today, there is an increasing number of cases of harsh conditions (time, temperature, humidity and the like) during the period from fill packaging/heat sterilization to consumption, as has been described above. For example, foods that have been filled and packed in Southeast Asia, South America, etc. are transported to Europe and the United States, Japan, etc. Therefore, a vacuum packaging pouch that maintains higher oxygen barrier properties after the vacuum packaging/heat sterilization than conventional ones is desired. In addition, a vacuum packaging pouch capable of withstanding heat sterilization under more severe conditions is desired.
Citation List
Patent Literature
Patent Literature 1: JP 5(1993)-318550 A
Patent Literature 2: JP 57(1982)-30745 B2
Patent Literature 3: JP 9(1997)-239911 A
Patent Literature 4: JP 2005-8160 A
Patent Literature 5: JP 2008-044617 A
Patent Literature 6: JP 2006-027695 A
Patent Literature 7: JP 2005-231701 A
Patent Literature 8: JP 2006-306083 A
Patent Literature 9: JP 11(1999)-314675 A
Patent Literature 10: JP 2005-119063 A
Patent Literature 11: JP 2006-036272 A
Patent Literature 12: JP 2007-008148 A